Methods for preventing loss of air in tires, especially tubeless tires, are well known to those skilled in the art. For example, U.S. Pat. Nos. 3,935,893 (Stang et al), 3,952,787 (Okado et al) and 4,064,922 (Farber et al) all disclose self-sealing tires and are representative of the state of the art. These disclosures generally use sealants that are semi-cured elastomeric materials having a certain degree of adhesion to the inside of a tire carcass or its air impermeability-enhancing layer. Various materials have been used in the past with varying degrees of success.
It has been found that when sealant is applied to the tire carcass prior to curing the tire, the sealant has a tendency to flow irregularly away from the application area of the tread and buttress. An additional problem is encountered in trying to prevent the tire from sticking to the molding equipment during molding of the tire because of the inherent tackiness of the sealant. Problems of this nature are often exaggerated due to the high temperatures used in the molding process. For these reasons, sealants are usually applied to the tire carcass after the tire itself has been formed and cured. However, this mode of operation requires additional steps that are both costly and waste energy. These steps include scrubbing and cleaning the inside of the tire carcass with a solvent or soap and water (see for example U.S. Pat. No. 3,935,893, column 4, lines 44-57). After cleaning, sealant may then be applied to the inside of the tire carcass and exposed to normal curing conditions (see also column 4, line 58 through column 5, line 23 of U.S. Pat. No. 3,935,893).
While prior art designs generally involve costly additional steps required during manufacture of self-sealing tires, there can also be difficulties involved with operation of such tires. When self-sealing tires are rotated at high speed, sealant can tend to flow towards the center portion of the tire away from buttress areas due to centrifugal forces. This can reduce protection of buttress areas against punctures.
In general, the prior art discloses self-sealing pneumatic tire constructions wherein the layer of sealant material is covered with a layer of impermeable material for the purpose of holding the sealant material in place during operation of the tire itself. An example of such a structure is U.S. Pat. No. 3,981,342 which discloses in FIG. 4 a layer of sealant material covered by a liner 25.
The disadvantage of this type of construction is that the sealant and air impermeable material holding the sealant in place must be adhered to the tire in a separate operation after the tire is molded and cured. This is because the sealant releases gases and expands when exposed to the high temperatures of tire molding and curing processes. This expansion and the gases will cause the impermeable material to blister and break leaving the sealant improperly distributed inside the tire.
Alternatively, a layer of sealing material can be applied to the tire carcass without any covering and this is disclosed in the above patent in FIG. 1. However, if the sealant is applied in this form, it is not held in position and will tend to flow as discussed above. Also, the sealant must be applied, again, after the tire has been molded and cured because the sealant would stick to tire building drums and other equipment during the steps of building the tire.